These studies are developing methods to quantitate the levels of fungal products in dust samples from water damaged buildings so that biomarkers of effect, such as fungal specific antibodies, can be correlated with biomarkers of exposure. A protocol for sample preparation and GC-MS/MS analysis to analyze mycotoxin in floor dust from water-damaged buildings has been adapted from a published method and the sample preparation procedure modified to improve extraction efficiency. By replacing silica solid phase extraction (SPE) cartridges and liquid-liquid extraction with polymeric reversed-phase SPE cartridges during sample preparation, recovery rates of spiked mycotoxin in sample extracts were significantly increased. A substantial matrix effect has been found to impact on the analytical method using building dust with the current internal standard (1,12-dodecandiaol). This matrix effect decreased recovery rates of mycotoxins in dust samples. To minimize this a matrix-matched calibration curve is now being used that allows for the detection of mycotoxins in most of the samples that were below limit of detection with a conventional calibration curve. NIOSH anticipates further improvement of the method by developing a C13-labeled verrucarol internal standard which will remove the matrix effect. This sotopically-labeled verrucarol internal standard for analysis of macrocyclic trichothecene mycotoxins using gas-chromatography/tandem mass-spectrometry (GC-MS/MS) is currently being developed.